Vacuum brake booster for automotive vehicles

ABSTRACT

A vacuum brake booster in which the guiding sleeve (14) for the push rod (29) has an annular ring which defines a cylindrical guiding surface (22) and is guided, in axial movements of the guiding sleeve, by a guide bore in the housing (10) of the control valve.

BACKGROUND OF THE INVENTION

The present invention relates to a vacuum brake booster for automotivevehicles and is of the type having a vacuum housing sealingly subdividedinto a vacuum chamber and a working chamber by an axially movable wallwhich is prestressed by a return spring. A mechanically actuable controlvalve connects the working chamber to the vacuum chamber or theatmosphere. The axially movable housing of the control valve is made ofthermoplastic material and accommodates, within an axial bore, arubber-elastic reaction disk which is abutted by a push rod fortransmitting the braking force to an actuating piston of a mastercylinder which is mounted on the vacuum housing on the vacuum side. Themovable wall is connected to the control valve housing and a guidesleeve, having a radial flange, serves to guide the push rod axially.

A vacuum brake booster of this type is disclosed in U.S. Pat. No.4,892,027 entitled "Vacuum Brake Power Booster for Automotive Vehiclesand Method for Its Manufacture" which corresponds to German PublishedPatent Application (DE-OS) No. 37 09 172. In the brake booster disclosedin U.S. Pat. No. 4,892,027, the radial flange of the guide sleeve isaxially supported within the bore of the control valve housing whichreceives the reaction disk and is retained axially, in a positivemanner, by a holding element connected to the control valve housing. Theholding element is formed either by a radial shoulder on the controlvalve housing or by radially inwardly directed projections formed on thecontrol valve housing or on a retaining ring, with the outside or insidesurface of the retaining ring being attached to the surface of thecontrol valve housing, for example, by ultrasonic or friction welding orby an adhesive. The arrangements just described can suffer frominaccuracies, might be unsafe, and can involve high cost.

In another vacuum brake booster disclosed in U.S. Pat. No. 4,898,073entitled "Vacuum Brake Force Booster for Use with Automotive Vehicles"which corresponds to German Patent Application No. 37 40 691.4, theguide sleeve has an axial extension which is provided to eliminate thedanger of damage to the control valve housing in the area of support forthe guide sleeve. Both the reaction disk and an abutting pressure plateare received in the axial extension of the guide sleeve which, in turn,is fitted and sealed in the axial bore of the control valve housing. Inthe brake booster disclosed in U.S. Pat. No. 4,898,073, the radialsupport of the axial extension of the guide sleeve is provided only bythe wall of the axial bore in the control valve housing in an area ofsmall wall thickness, so that the control valve housing can besusceptible to damage due to bending forces acting on the push rod.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a vacuumbrake booster which greatly mitigates the aforementioned disadvantagesand particularly the danger of damage to the control valve housing bytransverse forces.

This object is achieved, according to the present invention, by shapingthe radial flange of the guiding sleeve into a cylindrical guidingsegment which is axially guided within the control valve housing. Thisresults in a vacuum brake booster for automotive vehicles in which aconsiderable increase in operating reliability is achieved and excellentguidance of the push rod, as well as transmission of the highestretaining forces, is provided.

According to another aspect of the present invention, the cylindricalguiding segment has a radial collar on which the return spring issupported to retain the guiding sleeve in place.

In order to permit the use of smaller diameter reaction disks with thesame braking forces, according to another aspect of the presentinvention, the radial flange of the guiding sleeve is supported by ametallic insert containing the reaction disk as well as the flange ofthe push rod. This provides effective protection of the plastic controlvalve housing against the high pressures in the reaction disk andpermits closer fitting between the metallic insert and the flange of thepush rod as well as the ratio variation disk arranged between thecontrol valve piston and the reaction disk.

In order to avoid jamming of the push rod, in another embodiment of thepresent invention, the guiding sleeve has a cylindrical shape and thepush rod rests against the reaction disk by means of a pressure platewhich is separate from the push rod.

Finally, in order to permit quick evacuation of the working chamber ofthe vacuum brake booster constructed in accordance with the presentinvention, the radial flange has openings in the area where a vacuumchannel, which is formed in the control valve housing, ends.

Further details and advantages of a vacuum brake booster constructed inaccordance with the present invention will become evident from thefollowing description of two embodiments which will be explained in moredetail with reference to the accompanying drawings wherein correspondingparts are provided with like reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial longitudinal section of a first embodiment of avacuum brake booster according to the present invention; and

FIG. 2 is a partial longitudinal section of a second embodiment of avacuum brake booster according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The housing of the brake booster consists of two housing partsinterconnected at a joint by means of interlocking indentations. For thesake of clarity, only the brake-pedal-side housing part 7 is shown inpart. A booster piston 19 subdivides the interior of the housing into avacuum chamber 20 communicating, through a connection, with a vacuumsource (not shown) and a working chamber 23. The booster piston 19 has arolling diaphragm 18 in abutment therewith in the working chamber 23. Atwo-piece control valve housing 10 is connected with the booster piston19 and the rolling diaphragm 18. The rolling diaphragm 18 is clamped atthe joint 27 in a pressure-tight manner and, at its inner portion,encompasses the inside edge of the booster piston 19 and seals thebooster piston against the control valve housing 10. The cylindricalguide portion 4 of the control valve housing 10 protrudes from thebooster housing 7 and a bellows (not shown) protects the surface of thisportion of the control valve housing 10 against becoming soiled. Thecontrol valve housing 10 seals the working chamber 23 by means of aguide slide ring 5.

A control rod, composed of a piston rod 13 and a valve piston 16, isarranged to be axially displaceable within the control valve housing 10.The control rod is adapted for connection with a brake pedal of anautomotive vehicle via a fork head (not shown). The control valvehousing 10 also contains a valve arrangement 1, 9, and 12 actuated bythe valve piston 16 and, through channels 36 and 37, controls thepressure difference between vacuum chamber 20 and working chamber 23.The front part 2 of the control valve housing 10 is arranged in thevacuum chamber 20 and has a bore 3 within which a reaction disk 30 and apressure plate 17 are arranged. A push rod 29, abutting the pressureplate 17, actuates a master brake cylinder (not shown) fastened on thefront side of the booster housing.

A return spring 25, clamped between the front part 2 of the controlvalve housing 10 and the bottom of the booster housing, is provided forresetting the booster piston 19.

FIG. 1 shows the control assembly of the vacuum brake booster in therelease position, namely, in a position with the two chambers 20 and 23separated from each other. In this position, the two sealing seats 9 and12 abut the sealing surface of a poppet valve 1 which has a stop 8 onthe side facing away from the sealing surface. Stop 8, through a sleeve38, will sweep the guide portion 4. In the release position, the guideportion 4 rests with its collar 28 on the guide slide ring 5 and thesealing seat 9 on the control valve piston 16 is pushed by a piston rodreturn spring 11 against the sealing surface of the poppet valve 1.Simultaneously, the poppet valve 1 is prestressed, by means of acompression spring 15, toward the two sealing seats 9 and 12. The otherend of the compression spring 15 is supported on the sleeve 38. Also asecond compression spring 39 is provided which is supported, at one end,on a guide device 40 of the poppet valve 1 and, at an opposite end, onan annular surface 41 of the sleeve 38, to keep the two control valvehousing parts 2 and 4 apart.

In order to achieve precise guidance of the push rod 29, a guidingsleeve 14 is provided. The radial flange 21 of the guiding sleeve 14 issupported on an annular surface 26 of the front part 2 of the controlvalve housing and is shaped into an annular ring having a cylindricalguiding surface 22 which cooperates with a cylindrical portion 33 formedon the front part 2, so that the bending forces acting on the push rod29 are efficiently taken up. The radial flange 21 is provided withseveral openings 31 in the area where the vacuum channel 36 ends. Thereturn spring 25, supported on a radial collar 24 at the end of thecylindrical guiding surface 22, retains the radial flange 21 in place.Because the push rod 29 is separate from the pressure plate 17, theguiding sleeve 14 can be formed into a cylindrical shape as illustrated.

The reaction disk 30, in this embodiment of the invention, is arrangedin a section of the stepped bore 3 which faces the vacuum chamber 20. Aratio variation disk 6, which cooperates with the control valve piston16 and whose surface contacts the reaction disk 30, is arranged in thesecond, smaller-diameter section of the bore to govern the transmissionratio of the brake apparatus.

In the embodiment of the invention shown in FIG. 2, the push rod 29abuts the reaction disk 30 by means of a flange 34 formed integral withthe push rod 29. In this arrangement, the reaction disk 30, as well asthe flange 34, are contained by a metallic ring insert 32. The end ofthe insert 32 protruding from the axial bore 3 is provided with a radialexpansion 35 which serves as an abutment surface for the radial flange21 of the guiding sleeve 14, whereby the insert 32 is held in place. Inthis embodiment of the invention, the guiding sleeve 14 is conicallyshaped, so that its smaller diameter end remote from the control valvehousing 10 and 2, forms a first guiding point 42 for the push rod 29.The second guiding point 43 lies at the point of contact of the flange34 with the metallic insert 32. By enlarging the diameter of the guidingsleeve 14 at the end facing the control valve housing 10 and 2, jammingof the push rod 29 is mitigated.

What is claimed is:
 1. A vacuum brake booster for automotive vehiclescomprising:a vacuum housing sealingly subdivided into a vacuum chamberand a working chamber by a wall movable along an axis; a mechanicallyoperable control valve for connecting said working chamber with saidvacuum chamber or the atmosphere and having:(a) a thermoplastic materialhousing movable along said axis in response to the application andremoval of the braking force and having an axial bore extending alongsaid axis and a guide bore extending along said axis, (b) means forattaching said movable wall to said housing, and (c) valving means forpermitting and blocking fluid flow between said vacuum chamber and saidworking chamber in response to the application and removal of a breakingforce; a guiding sleeve movable along said axis and having:(a) a tubularportion extending along said axis, (b) a radial flange extending awayfrom said tubular portion, and (c) an annular ring extending from saidradial flange away from said axial bore and positioned within said guidebore of said control valve housing; a rubber-elastic pressure diskwithin said axial bore in said control valve housing and movable withsaid control valve housing; a push rod plate within said axial bore insaid control valve housing in abutment with said pressure disk andmovable with said control valve housing; and a push rod extending thoughsaid tubular portion of said guiding sleeve for movement along said axisand adapted for connection to an actuating piston of a master cylinderfor transmitting to the actuating piston, in response to movement ofsaid push rod plate, a braking force applied to said control valvehousing.
 2. A vacuum brake booster according to claim 1 wherein saidannular ring of said guiding sleeve defines a cylindrical surface andsaid guide bore in said control valve housing defines a cylindricalsurface.
 3. A vacuum brake booster according to claim 2 wherein saidguiding sleeve further includes a collar extending radially from saidannular ring of said guiding sleeve and said guide bore in said controlvalve housing has an annular recess within which said collar ispositioned.
 4. A vacuum brake booster according to claim 3 furtherincluding a spring bearing against said collar of said guiding sleeveand urging said collar against said annular recess in said guide bore insaid control valve housing.
 5. A vacuum brake booster according to claim1 wherein said radial flange is positioned against a surface of saidcontrol valve housing surrounding said axial bore.
 6. A vacuum brakebooster according to claim 5 wherein said push rod and said push rodplate are an integral unit and said tubular portion of said guidingsleeve has a conical inner surface with the smaller diameter end of saidtubular portion remote from said surface of said control valve housingagainst which said radial flange of said guiding sleeve is positioned.7. A vacuum brake booster according to claim 6 further including a ringinsert positioned within said axial bore in said control valve housingand within which said pressure disk and said push rod plate arepositioned.
 8. A vacuum brake booster according to claim 5 wherein saidpush rod and said push rod plate are separate components and saidtubular portion of said guiding sleeve has a cylindrical inner surface.9. A vacuum brake booster according to claim 7 wherein said radialflange of said guiding collar has a plurality of openings through whichfluid flows when said vacuum chamber and said working chamber areconnected.
 10. A vacuum brake booster according to claim 8 wherein saidradial flange of said guiding collar has a pluarlity of openings throughwhich fluid flows when said vacuum chamber and said working chamber areconnected.